Venous thrombosis of the lower limbs with particular reference to bed-rest

Venous valve hypoxia as a possible mechanism of deep vein thrombosis: a scoping review

INTRODUCTION

The pathogenesis of deep vein thrombosis (DVT) has been explained by an interplay between a changed blood composition, vein wall alteration, and blood flow abnormalities. A comprehensive investigation of these components of DVT pathogenesis has substantially promoted our understanding of thrombogenesis in the venous system. Meanwhile, the process of DVT initiation remains obscure. This systematic review aims to collect, analyze, and synthesize the published evidence to propose hypoxia as a possible trigger of DVT.

EVIDENCE ACQUISITION

An exhaustive literature search was conducted across multiple electronic databased including PubMed, EMBASE, Scopus, and Web of Science to identify studies pertinent to the research hypothesis. The search was aimed at exploring the connection between hypoxia, reoxygenation, and the initiation of deep vein thrombosis (DVT). The following key words were used: "deep vein thrombosis," "venous thrombosis," "venous thromboembolism," "hypoxia," "reoxygenation," "venous valve," and "venous endothelium." Reviews, case reports, editorials, and letters were excluded.

EVIDENCE SYNTHESIS

Based on the systematic search outcome, 156 original papers relevant to the issue were selected for detailed review. These studies encompassed a range of experimental and observational clinical research, focusing on various aspects of DVT, including the anatomical, physiological, and cellular bases of the disease. A number of studies suggested limitations in the traditional understanding of Virchow's triad as an acceptable explanation for DVT initiation. Emerging evidence points to more complex interactions and additional factors that may be critical in the early stages of thrombogenesis. The role of venous valves has been recognized but remains underappreciated, with several studies indicating that these sites may act as primary loci for thrombus formation. A collection of studies describes the effects of hypoxia on venous endothelial cells at the cellular and molecular levels. Hypoxia influences several pathways that regulate endothelial cell permeability, inflammatory response, and procoagulation activity, underpinning the endothelial dysfunction noted in DVT.

CONCLUSIONS

Hypoxia of the venous valve may serve as an independent hypothesis to outline the DVT triggering process. Further research projects in this field may discover new molecular pathways responsible for the disease and suggest new therapeutic targets.

A Comprehensive Review of Risk Factors and Thrombophilia Evaluation in Venous Thromboembolism

Venous thromboembolism (VTE), which encompasses deep vein thrombosis (DVT) and pulmonary embolism (PE), is a significant cause of morbidity and mortality worldwide. There are many factors, both acquired and inherited, known to increase the risk of VTE. Most of these result in increased risk via several common mechanisms including circulatory stasis, endothelial damage, or increased hypercoagulability. Overall, a risk factor can be identified in the majority of patients with VTE; however, not all risk factors carry the same predictive value. It is important for clinicians to understand the potency of each individual risk factor when managing patients who have a VTE or are at risk of developing VTE. With this, many providers consider performing a thrombophilia evaluation to further define a patient's risk. However, guidance on who to test and when to test is controversial and not always clear. This comprehensive review attempts to address these aspects/concerns by providing an overview of the multifaceted risk factors associated with VTE as well as examining the role of performing a thrombophilia evaluation, including the indications and timing of performing such an evaluation.

Prevalence and factors related with venous thromboembolism in patients admitted to the critical care units: A systematic review and meta-analysis

OBJECTIVE

Venous thromboembolism is one of the most common cardiovascular disorders in the any intensive care units (ICUs), which annually leads to death and imposes great costs on patients and society worldwide. The present study was conducted with the aim of determining the prevalence and factors related to venous thromboembolism in the ICUs as a systematic review and meta-analysis.

METHODS

The current study was conducted in international databases, on all descriptive and analytical studies and clinical and semi-experimental trial studies, without time limit until November 2, 2021. The present study was designed and implemented based on PRISMA guideline. The quality of the studies was checked using STROBE checklist and meta-analysis was performed using CMA software.

RESULTS

Among the 3204 articles found, after the evaluations, 189 articles entered the full text review phase, and as a result, 38 articles were included in the study. The reported prevalence of thromboembolism was 1-45%. The prevalence of venous thromboembolism was 12% in overall. The chance of venous thromboembolism was higher in ICUs patients >57 years old and ICUs patients with a history of venous thromboembolism.

CONCLUSION

The results of this study showed that venous thromboembolism has a higher prevalence in ICUs patients in comparison to non-ICUs patients. It is recommended to nurses and healthcare staffs to provide accurate decision and care for prevention of venous thromboembolism and paying attention to the patient's warning signs, timely administration of anticoagulants, and monitor coagulation factors.

Appearance and Frequency of Deep Venous Thrombosis After Total Hip Arthroplasty

Objectives

Postoperative venous thromboembolism is an important peri-operative complication associated with total hip arthroplasty (THA). In particular, early detection of deep venous thrombosis (DVT) is important for the prevention of pulmonary embolism (PE). However, the methods and timing of examinations for DVT detection differ among the facilities. This study aimed to clarify the time, site, and frequency of DVT after THA.

Materials and Methods

Background characteristics including age, sex, body mass index, diagnosis, operation type, operation time, and anesthesia type were investigated in 348 patients who underwent THA at our hospital between April 2017 and April 2019. Blood tests were performed preoperatively and on postoperative days (POD) 0, 1, 3, 7, 14, and 21. Simultaneously, vascular ultrasonography was performed to investigate the time and site of thrombus occurrence before and after the surgery.

Results

DVT was observed in 27.2% of the patients on POD 21. The DVT-positive ratio was 9.4% (6/64) in males and 31.3% (89/284) in females. There was a significant difference between the groups (p = 0.0002). Patients in the DVT-positive group were significantly older than those in the DVT-negative group (73.0 ± 7.9 years vs. 63.3 ± 11.2 years, p = 0.0041). DVT mainly occurred in the soleal vein (74.7%). However, there was no significant difference between the operated and non-operated sides. In the DVT-positive group, thrombus occurred in 13.3% of preoperative cases, 20.0% on POD 0, 46.7% on POD 1, 13.3% on POD 3, 6.7% on POD 7, and 0% on POD 14 and 21.

Conclusions

Vascular ultrasonography showed that thrombus occurred most frequently in the soleal vein. Thrombus occurred in 66.6% of DVT-positive patients by POD 1, indicating that thrombus appeared very early after surgery. All thrombus cases were formed by POD 7.

Evaluating post-operative venous thromboembolism risk in urology patients using a validated risk assessment model

Background

Venous thromboembolism (VTE) is an important cause of post-surgical morbidity and mortality. This study aimed to apply a validated risk assessment model to evaluate the risk of post-operative VTE in urology patients.

Methods

This prospective descriptive observational study used the Caprini risk assessment model to evaluate VTE risk in patients planned for elective urology surgery at a tertiary Johannesburg hospital from January to June 2020.

Results

Two hundred and twenty-six patients with a mean age of 52 years were evaluated for post-operative VTE risk. The population was generally overweight, with a mean BMI of 26.3 kg/m2. The mean Caprini score was 4.42, reflecting a population at high risk for post-operative VTE. There was no statistically significant difference between males and females in this regard. On average, participants had three risk factors for post-operative VTE. Fifteen per cent of all patients were at low risk for VTE, while 40.3% of participants were categorised as moderate risk. The category with the highest percentage of participants (44.7%) was the high-risk category (Caprini score ≥ 5). High-risk patients undergoing oncology surgery comprised 16.8% of the population, and these patients may require extended duration pharmacological thromboprophylaxis to prevent VTE. The most clinically significant risk factors for post-operative VTE included age, obesity, malignancy and HIV infection.

Conclusion

Venous thromboembolism may be difficult to diagnose, and clinicians may underestimate the risk for it to develop. Risk assessment models, such as the Caprini score, are objective and a practical tool to guide the application of thromboprophylaxis. The application of the Caprini RAM in the elective urological surgery population at Chris Hani Baragwanath Academic Hospital yields similar results to studies performed elsewhere on similar surgical populations. Further research is required to evaluate whether the actual incidence of VTE correlates with the risk assessment in this population. Clinician compliance with the use of RAMs as well as the corresponding recommendations for prophylaxis may need to be evaluated. A validated risk assessment model which accounts for procedure-specific risks in urology may be useful.

Venous Thromboembolism in Major Orthopedic Surgery

Venous thromboembolism (VTE) is one of the most important complications in orthopedic surgery. Deep-vein thrombosis occurs frequently after surgery but has few clinical symptoms. The emboli formed may cause pulmonary thromboembolism, which is associated with a high mortality rate. The cost of medical care is doubled when VTE develops after surgery. Thus, it is imperative to focus on preventing VTE after major orthopedic surgery. The prevention method should be selected after considering the balance between VTE risk and bleeding risk attributable to drug prophylaxis. Physical prophylaxis, drug prophylaxis, or both should be selected. When performing VTE prophylaxis, the risks and merits of prophylaxis must be made clear to patients.

Application of the Caprini risk assessment model for deep vein thrombosis among patients undergoing laparoscopic surgery for colorectal cancer

Application of the Caprini risk assessment model was explored in patients with deep vein thrombosis (DVT) after laparoscopic colorectal cancer surgery.This study was a prospective study. The risk factors for DVT were assessed with a survey at baseline and on the morning of surgery, first day after surgery and sixth day by using repeated blood vessels on color Doppler ultrasound of the lower limbs, and the intraoperative and postoperative conditions were recorded.Among 148 surgical patients, 24.3% had asymptomatic DVT. According to the risk stratification, the incidence of DVT was related to the Caprini score (P < .001). The area under the curve of the Caprini model was 0.701 ± 0.047 (95% CI: 0.609-0.793, P<.001). The Youden index was 0.368, while the critical point was 10.5 in the Caprini model, corresponding to a sensitivity of 0.806 and a specificity of 0.563. Age, cardiovascular disease, intraoperative blood loss, postoperative fever, preoperative preparation, and hospital stay were higher in DVT patients than in patients without DVT. Moreover, the incidence of DVT in patients with a lithotomy position was higher than that in patients with a scissors position. In binary logistic regression analysis, the independent risk factors for DVT development were age, intraoperative blood loss, and preoperative preparation time.The Caprini model can be used for the prediction of venous thromboembolism in laparoscopic colorectal cancer surgery patients. The thrombosis risk assessment model must be established in line with patients undergoing endoscopic malignant tumor surgery.

Lower Activity and Function Scores Are Associated with a Higher Risk of Preoperative Deep Venous Thrombosis in Patients Undergoing Total Hip Arthroplasty

This study was performed to investigate the relationship between patients’ activity and function levels and the incidence of preoperative deep venous thrombosis (DVT) prior to total hip arthroplasty (THA). We retrospectively reviewed 500 patients admitted for primary or revision THA from July 2014 to October 2018. The diagnosis of DVT was confirmed using Doppler ultrasonography 1 month before THA. The patients’ activity and hip function were evaluated using several clinical scores: the Harris Hip Score (HHS), Oxford Hip Score (OHS), University of California Los Angeles (UCLA) activity score, and visual analog scale (VAS) score. Those scores and the medical history were examined for correlations with preoperative DVT using univariate and multivariate models. Univariate regression analysis showed that older age, current steroid use, anticoagulant use, a history of DVT, collagen disease, a lower UCLA activity score, and a lower OHS were associated with an elevated risk of preoperative DVT. The multivariate analyses showed that a higher UCLA activity score (odds ratio (OR): 0.0049–0.012) and higher OHS (OR: 0.0012–0.0088) were associated with a lower risk of preoperative DVT in each model. Age (OR: 1.07 in both models), current steroid use (OR: 9.32–10.45), and a history of DVT (OR: 27.15–74.98) were associated with a higher risk of preoperative DVT in both models. Older age, current steroid use, a history of DVT, a lower UCLA activity score, and a lower OHS were risk factors for preoperative DVT before THA, even when controlling for potential confounders. Patients exhibiting low activity and low function levels were more likely to have DVT, even before surgery.

Repeated assessments of physical activity and risk of incident venous thromboembolism

Essentials It is debated whether physical activity influences the risk of venous thromboembolism. The association was explored accounting for fluctuations in physical activity over time. Overall and in the elderly, physical activity was associated with 23% and 30% lower risk. A moderate proportion of the association (14-36%) was mediated via body mass index. SUMMARY: Background Whether physical activity influences the risk of incident venous thromboembolism (VTE) remains controversial, potentially because of methodological challenges, such as regression dilution bias. Objectives To investigate whether physical activity was associated with VTE risk, and explore the role of body mass index (BMI) as a mediator in a population-based cohort with repeated assessments of physical activity. Methods Participants (n = 30 002) attending one or more surveys of the Tromsø Study 4-6 (1994-1995, 2001-2002, and 2007-2008) were included and categorized on the basis of weekly physical activity. Incident VTE was registered until 31 December 2016. Hazard ratios (HRs) were calculated by the use of time-varying Cox regression models. The Aalen additive hazard model was used to quantify the total, direct and indirect effects of physical activity. Results There were 531 incident VTEs during follow-up. Physical activity (≥ 1 per week) was associated with a lower risk of VTE (HR 0.77, 95% confidence interval [CI] 0.64-0.92) than being inactive. The effect was most pronounced for those aged ≥ 65 years (HR 0.70, 95% CI 0.55-0.88) and for provoked events (HR 0.66, 95% CI 0.50-0.89). The differences in absolute risk between active and inactive individuals were - 0.42 (95% CI - 0.73 to - 0.14) and - 1.59 (95% CI - 2.74 to - 0.52) events annually per 1000 individuals in the total and elderly populations, respectively. A moderate proportion of the association (14-36%) was mediated via BMI. Conclusion Our findings suggest that regular physical activity is associated with a lower risk of VTE, particularly in the elderly. The association occurred at a low weekly amount of physical activity, and was only partly mediated by BMI.

Molecular and Clinical Issues about the Risk of Venous Thromboembolism in Older Patients: A Focus on Parkinson's Disease and Parkinsonism

Venous thromboembolism (VTE) is a common and potentially life-threatening condition which includes both deep-vein thrombosis (DVT) and pulmonary embolism (PE). VTE has a significant clinical and epidemiological impact in the elderly, and its incidence increases to more than 1% per year in older patients, suggesting the presence of specific age-related risk factors in this population. Immobilization seems to predominate as the main cause in patients admitted for medical acute illness in medicine wards, and there is evidence of a high risk in older patients with immobilization resulting from advanced forms of Parkinson’s disease (PD), regardless of the presence of an acute medical condition. In this review, we would to discuss the recent evidence on clinical, molecular and epidemiological features of VTE in older frail subjects focusing on patients with PD and parkinsonism. We also discuss some therapeutic issues about the risk prevention and we suggest a thorough comprehensive geriatric assessment that can represent an optimal strategy to identify and prevent the VTE risk in these patients.

A systematic review of mobility/immobility in thromboembolism risk assessment models for hospitalized patients

Hospitalized patients are at risk of venous thromboembolism (VTE) and prophylaxis is often suboptimal due to difficulty in identifying at-risk patients. Simple and validated risk-assessment models (RAMs) are available to assist clinicians in identifying patients who have a high risk for developing VTE. Despite the well-documented association of immobility with increased risk of thrombosis, immobility is not consistently defined in clinical studies. We conducted a systematic review of published VTE RAMs and used objective criteria to determine how the term immobility is defined in RAMs. We identified 17 RAMs with six being externally validated. The concept of immobility is vaguely described in different RAMs, impacting the validity of these models in clinical practice. The wide variability in defining mobility in RAMs precluded its accurate clinical application, further limiting generalization of published RAMs. Externally validated RAMs with clearly defined qualitative or quantitative terms of immobility are needed to assess VTE risk in real-time at the point-of-care.

Predictable factors of deep venous thrombosis in patients undergoing spine surgery

BACKGROUND

DVT is one of the major postoperative complications of joint replacement surgery of the lower extremity which can cause catastrophic complications such as pulmonary embolism. However, little is known about the incidence of DVT after spine surgery. The purpose of this study was to examine predictable factors of DVT after spine surgery.

METHODS

This study included 194 patients who underwent spine surgery (104 males, 90 females, mean age 65.7 years). Postoperative DVT was detected using duplex ultrasonography (DUS). Age, sex, BMI, operation time, amount of bleeding, preoperative ambulatory status, usage of instrumentation, and preoperative serum levels of D-dimer were compared between the DVT(+) and DVT(-) groups to establish predictors for postoperative DVT. Cut-off value of the preoperative level of D-dimer was calculated using ROC analysis.

RESULTS

Postoperative DVT was detected in 57 patients (29.4%). No patients showed clinical signs of DVT or pulmonary embolism. Sex, age, BMI, preoperative non-ambulatory status, and preoperative levels of D-dimer were significantly different between the DVT(+) and DVT(-) groups. However, age and BMI was not significantly different factor in logistic regression analysis. Cut-off value of preoperative D-dimer was 1.4 μg/ml.

CONCLUSION

It was suggested that perioperative application of DUS for detecting DVT in the lower extremities should be performed on patients undergoing spine surgery who are female, non-ambulatory, and with higher preoperative D-dimer serum level.

Incidence of venous thromboembolism in care homes: a prospective cohort study

BACKGROUND

Care home residents have venous thromboembolism (VTE) risk profiles similar to medical inpatients; however, the epidemiology of VTE in care homes is unclear.

AIM

To determine the incidence of VTE in care homes.

DESIGN AND SETTING

Observational cohort study of 45 care homes in Birmingham and Oxford, UK.

METHOD

A consecutive sample of care home residents was enrolled and followed up for 12 months. Data were collected via case note reviews of care home and GP records; mortality information was supplemented with Health and Social Care Information Centre (now called NHS Digital) cause of death data. All potential VTE events were adjudicated by an independent committee according to three measures of diagnostic certainty: definite VTE (radiological evidence), probable VTE (high clinical indication but no radiological evidence), or possible VTE (VTE cannot be ruled out). (Study registration number: ISTCTN80889792.) RESULTS: There were 1011 participants enrolled, and the mean follow-up period was 312 days (standard deviation 98 days). The incidence rate was 0.71 per 100 person years of observation (95% confidence interval [CI] = 0.26 to 1.54) for definite VTE, 0.83 per 100 person years (95% CI = 0.33 to 1.70) for definite and probable VTE, and 2.48 per 100 person years (95% CI = 1.53 to 3.79) for definite, probable, and possible VTE.

CONCLUSION

The incidence of VTE in care homes in this study (0.71-2.48 per 100 person years) is substantial compared with that in the community (0.117 per 100 person years) and in people aged ≥70 years (0.44 per 100 person years). Further research regarding risk stratification and VTE prophylaxis in this population is needed.

Endothelin-1 Gene Polymorphism and Its Level Predict the Risk of Venous Thromboembolism in Male Indian Population

Objectives:

Genes related to endothelial function are responsible for the regulation of vascular functions.

Aim:

The aim of this study is to investigate whether endothelial gene-associated polymorphism and their plasma levels can be used to predict the risk for venous thromboembolism (VTE).

Methods:

We studied 133 patients with VTE and 164 healthy controls. Endothelin (EDN) G8002A, EDN T1370G, EDN 3A/4A, eNOSG894T, angiotensin-converting enzyme I/D, vascular endothelial growth factor C936T, and endothelial cell protein C receptor A6936G polymorphism was genotyped by restriction fragment length polymorphism. Plasma levels of endothelin 1 (EDN1), endothelial nitric oxide synthase, and angiotensin-converting enzyme were measured by enzyme-linked immunoassay kit.

Results:

The genotype and allele frequency between control and patients with VTE were significantly altered only for EDN T1370G polymorphism. The plasma EDN1 concentration was relatively higher in patients with VTE ( P = .0017) compared to healthy controls and showed an association with the EDN1 gene polymorphism in male Indian population. Logistic regression model analysis for EDN T1370G indicated a significant association between EDN G allele and occurrence of VTE.

Conclusion:

The EDN1 gene polymorphism may play a significant role in predicting individual’s susceptibility toward VTE and its clinical progression.

Occurrence of Deep Vein Thrombosis among Hospitalized Non-Surgical Japanese Patients

OBJECTIVE

To estimate the frequency of deep vein thrombosis (DVT) among non-surgical inpatients, and to evaluate the D-dimer assay as a screening tool for DVT.

METHODS

Subjects were non-surgical inpatients aged 20 years or older who had been bedridden for at least 24 hours and had moderate-to-high risk factors for DVT. We assessed the presence of DVT by venous ultrasonography. Patients who received a diagnosis of venous thromboembolism (VTE) before admission, who had symptoms or findings of VTE at admission, or who had surgery or trauma within the past 3 months before admission were excluded.

RESULTS

DVT was confirmed in 96 of 525 patients (18.3%). In a logistic regression analysis, longer duration of hospitalization, higher D-dimer value, and history of cancer surgery were significantly associated with the occurrence of DVT. The D-dimer assay showed high sensitivity (96.1%) and high negative predictive value (97.6%).

CONCLUSION

Non-surgical inpatients with a long-term hospitalization or history of cancer surgery have a risk for DVT, and need to be considered for added DVT preventive measures as recommended in the prevention guidelines. In addition, the D-dimer assay is beneficial for the screening of DVT in medical practice.

Pathophysiology of venous thrombosis

In this chapter, an overview of some of the prominent risk factors that contribute to the pathophysiology of venous thrombosis will be discussed. In 1856, Dr Rudolf Virchow developed the concept outlining the genesis of intravascular thrombosis. Dr Virchow hypothesized that circulatory stasis due to interrupted blood flow, changes in the blood leading to blood coagulation, and irritation or damage to the vascular endothelium would initiate acute venous thrombus generation. Presently, it is known that these above-mentioned risk factors are influenced by increasing age, gender, and obesity. The current chapter will focus on recent preclinical and clinical investigations that will give the reader insight into the prothrombotic mechanisms that lead to acute venous thrombosis.

Short-term venous stasis induces fibrinolytic activation but not thrombin formation

AIM

Venous stasis is a well-known risk factor for the development of venous thromboembolism. It is likely that stasis increases the risk of thrombosis by inducing hypercoagulability via the hypoxic procoagulant activation of endothelial and mononuclear cells and the accumulation of activated clotting factors. However, increased rates of thrombin formation have not been demonstrated in response to venous stasis in vivo.

METHODS

In this study, we used the venous occlusion (VO) test to determine, if stasis triggers thrombin formation in healthy individuals (n=25) and patients with additional thrombotic risk factors, such as inherited thrombophilia (n=19) and symptomatic atherosclerosis (n=15). Thrombin formation was monitored by measuring plasma levels of free thrombin using a highly sensitive oligonucleotide enzyme capture assay (OECA) in addition to the plasma levels of prothrombin fragment 1+2 (F1+2) and thrombin-antithrombin-complexes (TAT). The plasma levels of activated protein C (APC) were additionally measured using an APC-OECA.

RESULTS

VO induced a significant (p<0.05) increase in the levels of tissue-type plasminogen activator and plasmin-α2-antiplasmin-complexes. In all three cohorts, the majority of samples obtained during VO showed no quantifiable thrombin or APC levels. Consistent with these findings F1+2 and TAT did not change.

CONCLUSIONS

We conclude that short-term venous stasis induces a profibrinolytic response due to the activation of endothelial cells, but not a prothrombotic response, even in the presence of additional thrombophilic risk factors. Furthermore, our results support the hypothesis that the stasis-induced profibrinolytic activation of endothelial cells occurs independently from thrombin formation.

[Incidence and distribution of 1026 lower limb venous thrombi diagnosed by ultrasonography in 3263 patients with cancer]

The study objective was to evaluate the incidence, characteristics and distribution of lower limb deep venous thrombi diagnosed by ultrasound among known cancer patients, in order to determine additional criteria that could be used to help select patients with unprovoked deep venous thrombosis caused by occult cancer.

PATIENTS AND METHODS

From January 2001 to May 2012, standardized report forms (n=38,424) were entered into a database. A total of 3263 report forms corresponding to cancer patients with suspected venous thrombo-embolic disease were selected from which 1026 cases of deep venous thrombosis were diagnosed by ultrasonography. Baseline characteristics, incidence, and anatomic distribution of venous thrombi were analyzed.

RESULTS

For 3263 patients with cancer, the venous thrombosis incidence was: total 31.4% (n=1026), proximal 14.5% (n=472), bilateral 8.5% (n=278) and multiple venous sites 4.6% (n=149). The rate of clinical suspicion of pulmonary embolism was 49.9% (n=1628). For 1026 patients with thrombosis, proximal thrombi were nearly as frequent as distal thrombi, with 17.6% (n=181) iliocaval thrombi. Gastrocnemial, popliteal and femoral veins were almost equally concerned by thrombosis with respective rates of 28.7% (n=278), 27.1% (n=294) and 25.6% (n=263). Superficial veins were concerned in 23.5% (n=241). Partial or floating clots occurred frequently in 4 localizations: common femoral, external iliac, femoral and popliteal veins.

CONCLUSION

Proximal, multiple, partial, mobile thrombi, and such unusual locations as gastrocnemial or superficial thromboses, are potentially indicators for selecting patients that may benefit from a cancer check-up because their venous thrombosis could be due to cancer.

Finding the origin of pulmonary emboli with a total-body magnetic resonance direct thrombus imaging technique

Pulmonary embolism is considered to originate from embolization of a deep-vein thrombosis, resulting in two manifestations of one disease: venous thrombosis. However, in up to 50% of patients with pulmonary embolism no deep-vein thrombosis is found with ultrasonography. An explanation for this low proportion is currently lacking. Other imaging modalities may increase the yield of detection of deep-vein thrombosis in the calf or in the abdominal region. Alternatively, not all pulmonary emboli may originate from deep-vein thromboses in the extremities. We searched for the origin of pulmonary emboli, by performing total-body magnetic resonance imaging-scans to visualize thrombi. Ninety-nine patients with a first pulmonary embolism confirmed by computed tomography underwent a magnetic resonance direct thrombus imaging-scan, a validated technique using endogenous contrast. Additionally, acquired and genetic risk factors were assessed. No thrombus was found in 55 patients, whereas a thrombus was identified in 44 patients. The commonest thrombus location was the lower leg; 12 patients had isolated calf vein thrombosis and five had isolated superficial vein thrombosis. A peripheral thrombus was found by magnetic resonance imaging in less than half of patients with pulmonary embolism. We propose several hypotheses to explain the absence of thrombi, such as a cardiac thrombus origin or embolization of the whole deep-vein thrombus. The possibility that pulmonary embolism arises de novo in the lungs, due to local inflammation-driven coagulation, needs to be considered.

All I want for coagulation

Evidence-based medicine underpins modern practice of medicine. This paper describes a fictional consultation between Santa Claus and a doctor regarding deep vein thrombosis (DVT) prophylaxis, giving a review of the evidence for DVT prophylaxis in travellers while exposing the difficulty in applying evidence to atypical clinical encounters. Medline and the Cochrane Library were searched, and guidelines reviewed. Keywords used were DVT, thromboembolism, deep vein thrombosis and air travel-related venous thromboembolism. All relevant studies found, have been included in this review, with additional studies identified from the references in these articles. In conclusion, compression stockings, with or without a one-off dose of either aspirin or heparin, are the most evidence-based approaches for prophylaxis in someone with established risk factors for DVT prior to a long-haul flight. Simple exercises should also be encouraged.

Analysis of flow and wall shear stress in the peroneal veins under external compression based on real-time MR images

As a widely accepted prophylaxis for deep vein thrombosis, the underlying mechanism of compression stocking still remains unclear. In this study, computational fluid dynamics was applied to in vivo data to provide quantitative insight into the hemodynamic response of the deep venous system to static external compression. The geometry and flow information of deep veins before and after compression was acquired from ten healthy volunteers using magnetic resonance imaging. Our results indicated that application of the compression stocking led to a small reduction in blood flow rate but a significant reduction in cross-sectional area of the peroneal veins in the calf, resulting in an increase in wall shear stress (WSS), but the individual effects were highly variable. The mean volume reduction of the deep veins was 58%, while the time-averaged WSS showed an average increase of 398% after compression (median 98%). The analysis also showed a strong linear correlation between the time-averaged WSS and mean blood velocity, suggesting that flow in the deep veins under the level of compression examined here can be approximated by Poiseuille's law despite local geometric variations. It is hoped that quantitative analysis of WSS in the deep venous system will aid in the future design and optimisation of the compression stocking.

Symptomatic venous thromboembolism in Asian colorectal cancer surgery patients

BACKGROUND

The occurrence of venous thromboembolism (VTE), manifesting as deep vein thrombosis (DVT) or pulmonary embolism (PE), after colorectal cancer surgery in Asian patients remains poorly characterized. The present study was designed to investigate the incidence of symptomatic VTE in Korean colorectal cancer patients following surgery, and to identify the associated risk factors.

METHODS

We retrospectively analyzed data from patients who developed symptomatic VTE after colorectal cancer surgery between 2006 and 2008. Deep vein thrombosis was diagnosed with Doppler ultrasound or contrast venography, and PE was identified with lung ventilation/perfusion scans or chest computed tomography. Thromboprophylaxis, including low-molecular-weight heparin, graduated compression stockings, and intermittent pneumatic compression, was used in patients considered at high risk of VTE.

RESULTS

Of the 3,645 patients who underwent colorectal cancer surgery, 31 (0.85%) developed symptomatic VTE. Of those 31 patients, 23 (74.2%) had DVT, 16 (51.6%) had PE, and 8 (25.8%) had both. Two patients died from PE. Univariate analysis showed that a history of VTE, pre-existing cardiovascular disease, respiratory disease, transfusions, postoperative immobilization time, and postoperative complications were associated with VTE (p < 0.05 for each). Multivariate analysis showed that a history of VTE, pre-existing cardiovascular disease, postoperative complication, advanced cancer stage, and postoperative immobilization time were risk factors for developing symptomatic VTE. The mean hospital stay was 18.3 days, and the mortality rate was 6.5%.

CONCLUSIONS

The incidences of symptomatic DVT and PE were found to be not low in Asian colorectal cancer surgery patients compared with Western countries. The risk factors for VTE were a history of VTE, pre-existing cardiovascular disease, postoperative complications, advanced cancer stage, and postoperative immobilization. Thromboprophylaxis should be strongly considered in patients with these characteristics. Large prospective randomized controlled trials should be conducted to further evaluate the risk of VTE in Asian patients, and to determine the optimal prophylaxis.

Role of tissue factor in venous thrombosis

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality worldwide. However, the mechanisms by which clots are formed in the deep veins have not been determined. Tissue factor (TF) is the primary initiator of the coagulation cascade and is essential for hemostasis. Under pathological conditions, TF is released into the circulation on small-membrane vesicles termed microparticles (MPs). Recent studies suggest that elevated levels of MP TF may trigger thrombosis. This review provides an overview of the role of TF in VTE.

Predictive and associative models to identify hospitalized medical patients at risk for VTE

BACKGROUND

Acutely ill hospitalized medical patients are at risk for VTE. We assessed the incidence of VTE in the observational International Medical Prevention Registry on Venous Thromboembolism (IMPROVE) study and derived VTE risk assessment scores at admission and associative VTE scores during hospitalization.

METHODS

Data from 15,156 medical patients were analyzed to determine the cumulative incidence of clinically observed VTE over 3 months after admission. Multiple regression analysis identified factors associated with VTE risk.

RESULTS

Of the 184 patients who developed symptomatic VTE, 76 had pulmonary embolism, and 67 had lower-extremity DVT. Cumulative VTE incidence was 1.0%; 45% of events occurred after discharge. Factors independently associated with VTE were previous VTE, known thrombophilia, cancer, age > 60 years, lower-limb paralysis, immobilization ≥ 7 days, and admission to an ICU or coronary care unit (first four were available at admission). Points were assigned to each factor identified to give a total risk score for each patient. At admission, 67% of patients had a score ≥ 1. During hospitalization, 31% had a score ≥ 2; for a score of 2 or 3, observed VTE risk was 1.5% vs 5.7% for a score ≥ 4. Observed and predicted rates were similar for both models (C statistic, 0.65 and 0.69, respectively). During hospitalization, a score ≥ 2 was associated with higher overall and VTE-related mortality.

CONCLUSIONS

Weighted VTE risk scores derived from four clinical risk factors at hospital admission can predict VTE risk in acutely ill hospitalized medical patients. Scores derived from seven clinical factors during hospitalization may help us to further understand symptomatic VTE risk. These scores require external validation.

Venous thrombosis in the elderly: incidence, risk factors and risk groups

The incidence of venous thrombosis (VT) increases sharply with age: it is very rare in young individuals (<1 per 10,000 per year) but increases to ∼ 1% per year in the elderly, which indicates that aging is one of the strongest and most prevalent risk factor for venous thrombosis. The cause of this steep age gradient is as yet, unexplained. The aim of this review was to provide an overview of studies on the effect of conventional risk factors as well as age-specific risk factors for thrombosis in the elderly. Limited data are available on risk factors for thrombosis in the elderly, i.e. all results are based on small study groups. Results indicate that, of the conventional risk factors, malignant disease, the presence of co-morbidities and the genetic risk factors factor (F)V Leiden and the prothrombin mutation seem to be associated with an increased risk of venous thrombosis. In the elderly, the population attributable risk (PAR) of malignancy is approximately 35%, for co-morbidities a PAR up to 25% is found, and the contribution of genetic risk factors to the thrombosis incidence is estimated to be 7-22%. Age-specific risk factors of thrombosis, i.e. endothelial dysfunction and frailty may be important in the explanation of the increased incidence of VT in the elderly. In conclusion, as aging is a major risk factor for thrombosis, further identification of the risk factors for thrombosis in the elderly is needed to elucidate the age gradient of the incidence of VT and to target preventive measures.

Venous thromboembolism: a clinical review

Venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism, represents a significant source of morbidity and mortality. It is readily diagnosed with noninvasive modalities when there is a clinical suspicion. Most patients presenting with signs and symptoms of DVT have well-known risk factors, such as a history of VTE, malignancy, recent illness, or immobilization. A subset of individuals with idiopathic VTE have no readily identifiable risk factors. Therapeutic anticoagulation is the cornerstone of management in all patients with VTE. Adjunctive measures, such as thrombolysis and the use of vena cava filters, are indicated in select cases. The ideal duration of anticoagulation is unknown, but is often maintained long-term in patients with acquired or inherited thrombophilia. Warfarin is the only oral anticoagulant approved by the US Food and Drug Administration. Warfarin carries a substantial annual risk of bleeding complications, requires ongoing monitoring, and has extensive drug-drug interactions, which are causes for concern in patients requiring long-term anticoagulation. Alternative oral anticoagulants, such as direct thrombin inhibitors and factor Xa inhibitors, are subjects of active research in alternative agents for oral anticoagulation, and have been recently approved for prophylaxis in Canada and the European Union.

Prevention of venous thromboembolism

Venous thromboembolism (VTE) is a preventable cause of significant morbidity and mortality in hospitalized patients, especially in the perioperative period. After identifying the risk factors, it is possible to stratify patients into groups based on their degree of risk for developing VTE. Methods available for the prevention of VTE vary in degree of intensity, efficacy, and side effects. The type of preventive measure used for each patient is based on matching the degree of risk for VTE with the intensity of prophylaxis, keeping in mind the risk-benefit ratio. This article discusses VTE prophylaxis relevant to oral and maxillofacial surgery patients.

Settling properties of venous blood demonstrated in the peripheral vasculature using susceptibility-weighted imaging (SWI)

PURPOSE

To evaluate the settling properties of venous blood in the peripheral vasculature during periods of immobility.

MATERIALS AND METHODS

Susceptibility-weighted imaging (SWI) was performed for nine subjects at two time points: within 10 minutes of entering the magnet and after 40 minutes spent stationary in the magnet. Changes in the phase and in the distribution of phase of the veins were used to draw conclusions about the separation of red blood cells from plasma over time.

RESULTS

Settling was observed to occur in eight of the nine subjects, the only exception being the youngest subject (18 years old). The bottom half of some veins was seen to darken while the top half showed little change often with a clear dividing line between the two. Phase values measured in the bottom layer were consistent with the layer consisting entirely of red blood cells. Settling was seen to increase with time spent stationary and to correlate with the size of veins in the calf.

CONCLUSION

Older subjects tended to have larger veins and consequently more settling of the red blood cells. Our results show that even 40 minutes of rest can easily lead to settling of the blood depending on the position of the leg.

Prospective analysis of risk factors and distribution of venous thromboembolism in the population-based Malmö Thrombophilia Study (MATS)

BACKGROUND

Despite venous thromboembolism (VTE) being a major cause of morbidity and mortality, there is still limited information on its prevalence and incidence in the general population.

OBJECTIVE

To evaluate risk factors, distribution and epidemiology of VTE in the Malmö area with 280,000 inhabitants.

METHODS

Patients diagnosed with VTE at Malmö University Hospital in 1998-2006 were invited to a prospective population-based study. Blood sampling and a questionnaire study could be performed in 70% of patients. Remaining 30% were excluded due to language problems, dementia, other severe disease, or unwillingness to participate.

RESULTS

During 1998-2006 1140 VTE patients (559 men [49%, age 62+/-16 years] and 581 women [51%, age 61+/-20 years]) were included. Deep venous thrombosis (DVT) occurred in 882 (77%), pulmonary embolism (PE) in 330 (29%), and both DVT and PE in 72 (6%). The most common acquired risk factors among VTE patients were hormone therapy (24% of female DVT patients and 19% of female PE patients), immobilisation (17% of DVT patients and 18% of PE patients), previous surgery (13% of DVT patients and 19% of PE patients), and concomitant malignant disease (12% of DVT patients and 11% of PE patients). A positive family history for VTE was obtained from 25% of DVT patients and 22% of PE patients. Yearly incidences of VTE, DVT and PE in Malmö were 66, 51, and 19/100.000, respectively.

CONCLUSION

Hormone therapy, immobilisation, previous surgery and concomitant malignancy were the most common acquired risk factors among VTE patients in this population-based study. The VTE-incidence was lower than in earlier epidemiological studies.

Global Risk Profile Verification in Patients with Venous Thromboembolism (GRIP VTE) in 5 Gulf Countries

Background: The Global Risk Profile Verification in Patients with Venous Thromboembolism was the first prospective multicenter registry conducted in Arabian Gulf countries to explore the epidemiology of venous thromboembolic (VTE) disorders and to provide data on diagnosis and disease management. Methods: Data on 242 patients with confirmed VTE were submitted between September 2003 and November 2003 from 28 contributing hospitals in the Arabian Gulf region. Differences between groups were assessed by the χ2test or Fisher exact test for categorical variables. The Student's t test was used for testing proportions. Results: The frequency of VTE cases is deep vein thrombosis (DVT), 187 (77.27%); pulmonary embolism (PE), 35 (14.46%); and DVT with PE, 20 (8.26%). The most common symptoms of DVT and DVT/PE patients were calf pain (72%), calf swelling (63.8%), and localized tenderness (52.2%). The most common symptoms in patients with PE alone and DVT/PE were dyspnea (83.6%), thoracic pain (69.1%), and cough (40%). Risk factors for VTE were immobilization (41.3%), age >65 years (28.9%), a history of VTE (20.7%), and trauma (19%). Among surgical interventions, orthopedic procedures induced the greatest number of VTE cases, followed by general surgery and gynecological procedures. Low-molecular-weight heparins were chosen to treat 33.7% of DVT cases, whereas unfractionated heparin was used in 21.9% of cases. Conclusion: VTE remains a common problem in medical and surgical patients in the Arabian Gulf states. Recognition of the common risk factors is of extreme importance to implement the appropriate prophylactic strategy according to the published guidelines.

Superficial venous interventions: assessing the risk of DVT

Objectives

Understand the potential consequences of deep vein thrombosis (DVT) in patients undergoing superficial venous interventions, the proper way to assess DVT risk in patients with superficial venous disease and the appropriate management of patients stratified by risk level.

Methods

Review of published literature

Results

Because DVT can have major long-term consequences, DVT risk should be assessed as a routine part of the preprocedure evaluation of venous disease. Chronic venous disease may have multiple contributing factors amenable to treatment in both the superficial and deep venous systems.

Conclusion

Superficial venous interventions should be deferred in patients at particularly high risk for DVT, but may be performed with appropriate countermeasures for DVT prophylaxis in patients at moderate risk.

The role of venous valves in pressure shielding

Background

It is widely accepted that venous valves play an important role in reducing the pressure applied to the veins under dynamic load conditions, such as the act of standing up. This understanding is, however, qualitative and not quantitative. The purpose of this paper is to quantify the pressure shielding effect and its variation with a number of system parameters.

Methods

A one-dimensional mathematical model of a collapsible tube, with the facility to introduce valves at any position, was used. The model has been exercised to compute transient pressure and flow distributions along the vein under the action of an imposed gravity field (standing up).

Results

A quantitative evaluation of the effect of a valve, or valves, on the shielding of the vein from peak transient pressure effects was undertaken. The model used reported that a valve decreased the dynamic pressures applied to a vein when gravity is applied by a considerable amount.

Conclusion

The model has the potential to increase understanding of dynamic physical effects in venous physiology, and ultimately might be used as part of an interventional planning tool.